1. Field of the Invention
The present invention relates to an optical proximity correction method, and more particularly, to an optical proximity correction method for making a contact hole pattern to which a bias rule is difficult to apply.
2. Description of the Related Art
As the demands for increasing the integration density of semiconductor devices has continued, the design rules impose physical restraints on the methods of forming these ever refined patterns. To achieve this end of producing ever smaller patterns, shorter wavelength from exposure sources have been exploited. However, these sources and shorter wavelengths do cause a number of difficulties in patterning in accordance to a design layout feature. As a result the pattern printed out on the resultant wafer may become unacceptably distorted from the originally intended pattern. As the patterns becomes finer, the light intensity likely increase to achieve the particular pattern which can adversely affect adjacent patterns due to the optical proximity effect where the pattern formed over the wafer has a different shape from a pattern of the layout on the design.
The optical proximity effect needs to be compensated because it can contribute to degrading the performance of the resultant semiconductor devices. An optical proximity correction refers to a technique used to correct or to compensate for the layout to be formed over the wafer. The optical proximity correction includes a rule-based optical proximity correction for correcting the layout based on rules of mask layout correction, and a model-based optical proximity correction for correcting a mask layout by predicting an image transcribed over the wafer based on mask pattern information and a wafer process condition. Particularly, in the model-based optical proximity correction, the optical proximity correction is performed by applying an etching model that uses a critical dimension (CD) data of a final pattern formed by an etching process in which a photoresist pattern is used as an etch mask. Thus, the optical proximity correction for the semiconductor device implemented with an actual final pattern provides an improved accuracy in the resultant final pattern.
Meanwhile, in a case of forming a contact hole pattern among various kinds of other patterns of the semiconductor device, pattern uniformity has a significant effect on the performance of a highly integrated semiconductor device. Therefore optical proximity correction for correcting the contact hole pattern is especially important and hence emphasized. However, the contact hole pattern has a higher mask error enhancement factor so that there is a higher probability that an error can occur when only using the more conventional optical proximity correction methods. Also, a final CD after the etching process can induce a variation in CD due to the density of patterns that exist in the vicinity of a targeted pattern. Therefore, when applying the above described model-based optical proximity correction method to the contact hole pattern, it is very difficult to perform a sufficiently accurate correction since the final CD of the contact hole pattern is changed.
FIG. 1a illustrates a contact hole pattern to which a bias rule is applicable according to the related art and FIG. 1b illustrates a contact hole pattern to which the bias rule is not applicable according to the related art.
As shown in FIG. 1a, a bias rule R for obtaining a CD (W) data of a final pattern 10 applies only in a case when there is an object pattern and a pattern adjacent thereto. In other words, based on a space S between two adjacent final patterns 10, the bias rule R can be determined to meet a final inspection critical dimension (FICD) of the final pattern. Therefore, the bias rule R determined as described above can be used to perform a more accurate optical proximity correction that uses the FICD of the final pattern.
However, as shown in FIG. 1b, when patterns 10′ are to be implemented are not adjacent and thus are not arranged in a straight row, it is difficult to apply the bias rule. Therefore, the FICD of the final pattern has a lower uniformity so that the etching model becomes inaccurate. Thus, the accuracy of the optical proximity correction of the conventional methods that using the etching model is degraded.